Force fit connecting elements of the type described above are known for instance as hexagon head fit bolts according to DIN 609. In a preferred application they are used as wheel studs. They then have a head that is often formed to be slanted on one side and which forms a stop in the fitting. The stop terminates the fitting process. Connected to the head is a shank with a comparatively smaller outer diameter, which has a force fit section on the side facing the head. The force fit section is formed to be a ground cylindrical surface. The force fit section is the thickest part of the shank, i.e. it has the largest outer diameter in the region of the shank. A relief groove is provided between the head and the shank. It is also possible to provide a transition radius at this position which necessitates a corresponding bevelling of the drill hole into which the force fit connecting element is fitted. The force fit section has an overmeasure, i.e., it is oversized, with respect to the corresponding drilled hole. Particularly in the case of wheel studs, a section with a fastening thread joins the force fit section on the shank, with the outer diameter of the fastening thread being smaller than the outer diameter of the force fit section. The slugs used in the production of such wheel studs have in the region of the shank a stepped outer diameter. In the region of the force fit section to be ground the largest diameter is provided, while in the region of the fastening thread to be formed a smaller diameter is used. A tapered transition section is provided in between these two sections.
These known force fit connecting elements have a number of disadvantages. In order to stay within the required tolerances in the region of the overmeasure, the force fit section has to be finished by a grinding process. This grinding process is, on the one hand, elaborate and requires the use of additional material which is ground off, on the other hand. In the transition region between the force fit section and the head a relief groove is necessary if the corresponding drill hole has no bezel. This relief groove is usually made by machining, which together with the grinding makes the production more expensive. Such force fit connecting elements not only have a relatively high weight, but also require a higher starting weight than the weight of the finished part. In the production of the connecting element stepped slugs have to be used, which require an additional work step as compared to slugs with a continuous diameter of the shank. During the axial fitting of the force fit connecting element into the corresponding drilled hole of the work piece, especially the hub of a wheel, the use of a joining aid becomes necessary, which ensures that the force fit connecting element is guided and aligned axially so that the axis of the drilled hole and the axis of the wheel stud is concentrically aligned. Still, there is the danger of material displacement during the fitting, since the force fit section is oversized with respect to the drilled hole. The force fit connecting element has no centering aid, since the tapered transition section of the slug with the stepped shank is covered by the usually rolled fastening thread. Occasionally a seizing is observed during the axial fitting. Such seizing effects, which may ultimately be overcome by the axial force, lead to permanent damage of the force fit connecting element as well as the corresponding work piece with the drilled hole, so that both pieces cannot be used again.
There are further force fit connecting elements known in the art whose force fit section does not consist of a ground cylindrical surface area, but in which the force fit section has knurls, i. e. protruding ribs or ridges, which are axially aligned on the surface of the force fit section. The axial alignment of the knurls, i.e. parallel to the axis of the force fit connecting element, is necessary in order to avoid any turning motion of the force fit connecting element during the axial fitting into the drilled hole. Next to the elaborate production of such force fit connecting elements a major disadvantage is that they are not reusable. The knurling furrows itself into the drilled hole during the axial fitting and is plastically deformed. When this occurs the knurling does not fulfill the necessary tolerances at its outer diameters and the force fit connecting element is not reusable. The drilled hole of the corresponding work piece is also plastically deformed by the furrows, so that the matching piece of the force fit connecting element is also not reusable. In contrast to this, force fit connecting elements of the generic type with force fit sections on a cylindrical surface area are reusable. Here the work piece with the drilled hole is also reusable, as long as no seizing effects occur during the fitting.
Furthermore, so-called extension fit bolts are known, however the present invention is not concerned with these. Extension fit bolts, as they are known from the DE-PS 35 21 755, DE-OS 21 43 784, and EP 0 144 503 B1, all have undermeasure, i.e., are undersized with respect to the drilled hole in the region of their extension fit section. Furthermore, such connecting elements serve to connect two parts to each other in which the object is to center the two drilled holes of the two parts with respect to each other. The extension fit section is freely movable in the drilled hole under a corresponding axial force. A turning of the extension fit bolt must not be hindered. Extension fit connecting elements are either screwed in or inserted and then secured by a nut. The known extension fit connecting elements have either a slim shaped shank or a helical profile or circumferential swellings or ribs in the region of the extension section. By this the necessary extension function is obtained in the region of the extension fit section. The centering function for the two parts to be connected to each other is also obtained by the extension fit section, through which there is always some clearance during the joining, though. Therefore extension fit connecting elements are fundamentally different from the generic force fit connecting elements.